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How to Detect or Measure Electrical Voltage at / in a Building using a VOM, DMM, or Voltage Detector
- Voltage Measurement Equipment Types: How to Determine Electrical Voltage (240V/120V) using a neon tester, a VOM, DMM, Volt Meter, or Voltage Detector pen
- Photographs & properties of electrical test equipment useful for a building inspector, electrical inspector, contractor, or homeowner
- Use a Volt-Ohm meter VOM, Digital multi meter DMM or multimeter to measure the electrical voltage and amperage of an electrical service or at individual electrical circuits in a building
- Greenlee® GT-16 adjustable voltage detector, Tic Tracer Tif 300cc voltage detector, clamp-on or snap-around ammeter or digital multimeter properties & applications
- List of Electrical Test Instruments, VOMs, DMMs, Voltage Detectors: Manufacturers & Sources
- Questions & answers about how to detect or measure voltage at electrical wiring or electrical devices.
- References
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Electrical voltage detection and measurement methods & tools: this article describes how to safely use digital multimeters(DMMs), Volt-ohm meters (VOMs), neon testers to check for live electrical circuits and to measure electrical system voltage and amperage levels. For measuring amps or electrical current, see AMPS MEASUREMENT METHODS. For details about connecting probes and setting function and level switches on VOMs and DMMs, see DMM Digital Multimeter, How to Use. Also see USING DMMs VOMs SAFELY as well as SAFETY for ELECTRICAL INSPECTORS.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Voltage Test Equipment Types: How to Determine Electrical Voltage (240V/120V) using a neon tester, a VOM, DMM, Volt Meter, or Voltage Detector pen
Instruments as simple as the neon-tester shown here or a digital multimeter (DMM), or an analog volt meter (volt-ohm meter) such as
those made by Triplett, Fluke, Simpson and Sperry can be used to measure the voltage level between the two power
feed lines to confirm the presence of 240 Volt service. (Some versions of this equipment can also be configured to measure amperage or amps).
Using a DMM, analog volt meter, or a neon tester, voltage between the two apparently "hot" wires
in the panel will confirm 240-volt service. If only one cable is "hot" (testing cable to ground) it is a 120 V system. If both cables are "hot" to ground but there is no voltage between them it is
a 120V system which has been "split" to look like 240V but it is not 240V.
What's the difference between using a neon tester (shown at left) and using a VOM or digital voltage meter?
A neon tester, containing just a light bulb, simply indicates the presence of live voltage but not the actual voltage level. A volt meter is required to test for other voltage levels or to determine the actual voltage level as well as to check for voltage that may vary over time. |
Safety Warning: The ASHI Standards of Practice and other home inspection standards for electrical inspections do not require the inspector to insert any instrument into the service panel. Therefore this testing is optional.
It's also a dangerous procedure that can damage electrical equipment or worse, cause electrical shock, or even death, and should not be undertaken unless the person conducting the examination is trained and competent to avoid electric shock. If the inspector is not trained for this procedure
s/he should never insert any instrument or tool into electrical equipment. See Safety Hazards and Safe Inspection
Procedures at Residential Electric Panels.
- An ammeter measures electrical current. Our photo at left shows a multi-meter that can measure amps as well as serve ad a VOM - a volt-ohm volt meter.
Details of using an ammeter to measure building, individual circuit, or individual electrical appliance amps are found at AMPS MEASUREMENT METHODS.
- A voltage detector uses a light, sound, or both to indicate the presence of live electrical voltage
- A voltmeter measures the potential difference (voltage) between two points
- An ohmmeter measures resistance. An ohm meter measures resistance in a circuit or on a component and is not normally connected to a circuit carrying live voltage.
In this article we provide photographs and descriptions of each of these types of electrical test instruments. At DMM Digital Multimeter, How to Use we explain the function and level settings and probe connections needed when using a VOM or DMM to measure voltage (as well as when measuring current or resistance). |
Photographs & properties of electrical test equipment useful for a building inspector, electrical inspector, contractor, or homeowner
If you're unsure about the definitions of amps, volts, ohms, resistance, watts, etc. See DEFINITIONS of ELECTRICAL TERMS.
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A voltage detector of voltage sensor detects the presence of live AC voltage (some equipment also detects DC voltage), with a sensitivity typically between 5 and 1000 Volts. This equipment can sense the presence of live electrical devices or wiring without touching the device or wire.
Shown here (left) is the Greenlee® GT-16 adjustable voltage detector. Greenlee and other manufacturers recommend that you test the operation of the voltage detector on a known live circuit both before and after using it to test for the presence of electrical voltage at a wire or device. This device uses an AAA battery and has a sensitivity adjustment (the yellow dial in the center of the green patch on the device).
Some voltage sensors such as the FCB Voltage Pen operate without requiring a battery.
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Tic Tracer Tif 300cc voltage detector - properties & special uses: A different sort of voltage sensor detects the presence of live AC voltage is shown at left, the Tif 300cc Tic Tracer. Depending on the version, this instrument does not use an LED or neon bulb but emits a buzzing or "ticking" noise at a varying rate depending on how close it is held to a voltage source and also varying by voltage level.
Turning the instrument on gives a slow electronic tic-tic sound at a regular rate. Holding the sensor tip close to an electrical outlet or even along an electrical wire connected to such a receptacle results in an increase in the tic rate of the instrument.
And with even a limited amount of practice you can quickly learn to recognize the much faster tic rate (really a buzz) that the TIF makes when held close to a 240V circuit in comparison with a 120V electrical circuit.
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Unlike the elegantly simple neon tester, and more like the Greenlee® GT-16, the TIF Tic Tracer does not need direct contact between sensor pins and live electrical contacts in order to detect the presence of electrical voltage (photo, above left).
But unlike the Greenlee® GT-16 that needs to be very close to an electrical circuit or component in order to indicate the presence of voltage, the TIF Tic Tracer 300cc can sometimes detect the presence of electrical wires behind drywall (depending on the depth of wires inside the wall cavity and other factors) - as we illustrate in our second Tif 300cc photo, shown at left.
Watch out: the sensor tip of the Tif Tic Tracer is also sensitive to static electricity and possibly to vibration. If you rapidly swipe the sensor tip along the surface of a wall the instrument will sound wildly - an effect we once used to castigate an aggressive bystander.
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- A multimeter or DMM combines these functions into one piece of equipment and is often called a VOM or volt-ohm meter. Our little VOM/DMM shown at left is being used to check for voltage at an electrical receptacle. If you click and enlarge the photo you can see the meter reading.
- A neon tester simply measures for the presence of live electrical power as we demonstrated above.
- A continuity tester is a simple substitute for a more sophisticated ohm meter, and is used simply to confirm that there is electrical continuity on a circuit, that is,
that it is not interrupted by a switch or open connection.
Some simple ohm-meters or multimeters include a switch position that emits a tone if there is good electrical conductivity (low resistance) between the two points being touched by the probes.
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Analog VOMs - Volt-Ohm-Milliameters
- A VOM or volt-ohm meter may also be found in an analog form such as our favorite and now a collectors-item little Jensen VOM that we've used for nearly 30 years. Here our photo shows the Jensen analog VOM with its probes attached but not connected to anything.
In 30 years of use we needed one repair of this instrument - an internal fuse which we couldn't find locally. In analog VOMs such as this unit there is typically a very low-amperage fuse whose function is to protect the meter movement from damage.
On contacting Jensen Corporation, the company kindly sent us a few spare fuses. The total repair bill? $0.00.
This little VOM, ca 1985, is about 1/8 the size of the Simpson 260, ca 1958, described just below.
Simpson produces a wide range of test instruments including analog VOMs that can be used to measure resistance (ohms), direct current, alternating current, and even decibels. |
 Simpson Analog VOMs
Simpson produces a wide range of test instruments including analog VOMs that can be used to measure resistance (ohms), direct current, alternating current, and even decibels. Shown here is the Simpson Model 260 Series III Volt-Ohm Milliammeter produced ca 1958 and in use by its owner Paul Galow since ca 1959. This VOM is much larger than the compact devices in wide use today, having a meter display width of 4 1/2".
The device is also quite durable. Mr. Galow reports having to perform two maintenance chores on the instrument, replacing a battery and replacing a soldered-in-place fuse whose function is the protection of the meter movement.
Watch out: don't confuse a volt-ohm-milliameter with clamp-on ammeteres (described next). The Amps measurement range of this Simpson Model 250 VOM is 1MA to 500MA - not at all in the range of household appliances or larger equipment. For higher ampacity measurements you will need an ammeter such as the device described just below. See this circuit diagram of the Smipson 260. |
Amperage or current measurements using clamp on or snap around digital ammeters, DMMs, & (some) VOMs
- At left we are measuring the current draw in amps for the charging block of a laptop computer. Shown is Sperry's Digisnap DSA-500 snap-around digital multimeter.
Details about using a clamp-on or snap around ammeter are at see AMPS MEASUREMENT METHODS.
Notice that the electrical wire was split so that the clamp-on ammeter's jaws surround just one of the two electrical wires. The transformer jaws or "clamp" must surround just one of the two 120V wires supplying the electrical device.
Also notice that we did not disturb nor damage the electrical wire insulation itself - doing so is dangerous and risks equipment damage or dangerous electrical shock as we cite just above.
At the moment of our measurement this electrical device was drawing 0.29A at 120V.
For an accurate calculation of actual energy consumed that includes the effects of AC current and power factors, see Definition of Power Factor, Real Power. |
List of Electrical Test Instruments, VOMs, DMMs, Voltage Detectors: Manufacturers & Sources
- Actron DMMs & VOMs, Website: http://www.actron.com/
- Digisnap DSA-500 snap-around digital multimeter, A.W. Sperry Instruments Inc., 2150 Joshua's Path, Suite 202, Hauppage NY 11788, Tel: 800-645-5398, Email: cat@awsperry.com, Website: www.awsperry.com
- Equus Multimeters by Innova, Equus Products, Inc., 17352 Von Karman Ave., Irvine, CA 92614, U.S.A., Tel: 714-241-6800, Website: http://www.equus.com/
- ExTech DMMs & VOMs, ExTech Corp. a FLIR company, Extech Instruments Corporation,
9 Townsend West,
Nashua, NH 03063,
U.S.A., Email: support@extech.com, Tel: 877-239-8324 Option 3, Website: http://www.extech.com
- Fluke Corporation, 6920 Seaway Blvd, Everett, WA 98203, USA, PO Box 9090 Everett, Washington 98206, Tel: +1(425) 347-6100, Technical support: 1(800) 44-FLUKE (1(800) 443-5853), Website: www.fluke.com,
Fluke Europe B.V,
PO Box 1186 Eindhoven, The Netherlands, Tel: +31 (0)40 2 675 200 +31 (0)40 2 675 222, Website: www.fluke.eu
- Fluke India: TTL India Pvt. Ltd. (A Fluke Company),
Deodhar Center,
424, Marol Maroshi Road,
Andheri (E),
Mumbai, 400076, Tel: 1 800 209 9110, Email: info.india@fluke.com, Website: http://www.fluke.com/fluke/inen/products/Digital-Multimeters.htm
- Digital 287/289 Digital Multimeter, Users Manual, retrieved 9/5/21, original source: http://assets.fluke.com/manuals/287_289_umeng0200.pdf, [copy on file as Fluke_287_289_umeng0200.pdf]
- Jensen VOMs, no longer available
- Mastech VOMs and DMMs (made in China), Shanghai Hihua V&A Instrument Company, 881 Ye Cheng Road Jia Ding District, Shanghai 201821, China, Email: mastech@vip.sina.com, Tel: +86 21 69523164 +86 21 69523225, Website: http://www.mastech.com.cn/
- Simpson Electric, P.O. Box 99, 520 Simpson Avenue, Lac du Flambeau, WI 54538-0099 Tel: 715-588-3311, customer service: 715-588-3947, Email: support@simpsonelectric.com, Website: www.simpsonelectric.com/
- Simpson 260® Series 6XLM
Volt-Ohm-Milliammeter Instruction Manual, retrieved 9/5/2012, original source: http://www.simpsonelectric.com/uploads/File/datasheets/260-6xlm.pdf, [copy on file as Simpson_260-6xlm.pdf]
- tif 300cc Tic Tracer voltage detector, Tif Instruments Inc., 9101 NW 7th Avenue, Miami, Florida 33150
- Greenlee® GT-16 adjustable voltage detector, Greenlee Textron Inc., Website: greenlee.com, Tel: 800-435-0786 , Email: techsupport@greenlee.textron.com,
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- The Original Authors: Alan Carson is an ASHI Member, national home inspection educator, author and building failures researcher in Toronto, Ontario.
Daniel Friedman, an original author of this article and the editor and producer of InspectAPedia where this article now appears is an ASHI Member, first ASHI Technical Committee chairman, editor and publisher of the ASHI Technical Journal, licensed home inspector, educator, and building failures researcher in Poughkeepsie, NY.
Robert Klewitz is a licensed professional engineer, a professional home inspector, an ASHI Member, and has served on the ASHI Technical Committee as well as in other ASHI activities. His practice is in Issaquah, WA.
- ASHI Technical Journal, Vol. 2. No. 1, January 1992, "Determining Service Ampacity," Dan Friedman and Alan Carson,
and the
- ASHI Technical Journal, Vol. 3. No. 1, Spring, 1993, "Determining Service Ampacity - Another Consideration," Robert L. Klewitz, P.E.,
with subsequent updates and additions to the original text ongoing to 2/19/2006. Reprints of the originals and reprints of the Journal are available from ASHI, the American Society of Home Inspectors www.ashi.com.
- [4] Digisnap DSA-500 snap-around digital multimeter, A.W. Sperry Instruments Inc., 2150 Joshua's Path, Suite 202, Hauppage NY 11788, Tel: 800-645-5398, Email: cat@awsperry.com, Website: www.awsperry.com
- [5] Fluke Corporation, 6920 Seaway Blvd, Everett, WA 98203, USA, PO Box 9090 Everett, Washington 98206, Tel: +1(425) 347-6100, Technical support: 1(800) 44-FLUKE (1(800) 443-5853), Website: www.fluke.com,
Fluke Europe B.V,
PO Box 1186 Eindhoven, The Netherlands, Tel: +31 (0)40 2 675 200 +31 (0)40 2 675 222, Website: www.fluke.eu
- Fluke India: TTL India Pvt. Ltd. (A Fluke Company),
Deodhar Center,
424, Marol Maroshi Road,
Andheri (E),
Mumbai, 400076, Tel: 1 800 209 9110, Email: info.india@fluke.com, Website: http://www.fluke.com/fluke/inen/products/Digital-Multimeters.htm
- Digital 287/289 Digital Multimeter, Users Manual, retrieved 9/5/21, original source: http://assets.fluke.com/manuals/287_289_umeng0200.pdf, [copy on file as Fluke_287_289_umeng0200.pdf]
- [6] Simpson Electric, P.O. Box 99, 520 Simpson Avenue, Lac du Flambeau, WI 54538-0099 Tel: 715-588-3311, customer service: 715-588-3947, Email: support@simpsonelectric.com, Website: www.simpsonelectric.com/
- Simpson 260® Series 6XLM
Volt-Ohm-Milliammeter Instruction Manual, retrieved 9/5/2012, original source: http://www.simpsonelectric.com/uploads/File/datasheets/260-6xlm.pdf, [copy on file as Simpson_260-6xlm.pdf]
- [7] tif 300cc Tic Tracer voltage detector, Tif Instruments Inc., 9101 NW 7th Avenue, Miami, Florida 33150
- [8] Greenlee® GT-16 adjustable voltage detector, Greenlee Textron Inc., Website: greenlee.com, Tel: 800-435-0786 , Email: echsupport@greenlee.textron.com,
- [9] Jensen VOMs, no longer available
- [10] Mastech VOMs and DMMs (made in China), Shanghai Hihua V&A Instrument Company, 881 Ye Cheng Road Jia Ding District, Shanghai 201821, China, Email: mastech@vip.sina.com, Tel: +86 21 69523164 +86 21 69523225, Website: http://www.mastech.com.cn/
- [11] Equus Multimeters by Innova, Equus Products, Inc., 17352 Von Karman Ave., Irvine, CA 92614, U.S.A., Tel: 714-241-6800, Website: http://www.equus.com/
- [12] Actron DMMs & VOMs, Website: http://www.actron.com/
- [13] ExTech DMMs & VOMs, ExTech Corp. a FLIR company, Extech Instruments Corporation,
9 Townsend West,
Nashua, NH 03063,
U.S.A., Email: support@extech.com, Tel: 877-239-8324 Option 3, Website: http://www.extech.com
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com 11/06
- Douglas Hansen, Robert Stead. Mark Cramer. Photographs: Daniel Friedman.
- N. Srinivasan, MSEE, is a senior member of IEEE with 30 years experience in the electrical industry. Mr. Srinivasan is in Vienna VA.
- Louis P. Babin generously contributed technical editing about the effects of doubling ampacity in an electrical circuit (September 2007)
- Paul Galow - technical consultant on networking, LAN design, applications support. Galow Consulting Services, 914-204-1749, email: paulgalow@galowconsulting.com
- Rust and Corrosion in Electrical Panels, A Study and Report on Frequency and Cause for Electrical and Home Inspectors at Residential Electric Panels
- "Electrical System Inspection Basics," Richard C. Wolcott, ASHI 8th Annual Education Conference, Boston 1985.
- "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
- "How to plan and install electric wiring for homes, farms, garages, shops," Montgomery Ward Co., 83-850.
- "Simplified Electrical Wiring," Sears, Roebuck and Co., 15705 (F5428) Rev. 4-77 1977 [Lots of sketches of older-type service panels.]
- "Home Wiring Inspection," Roswell W. Ard, Rodale's New Shelter, July/August, 1985 p. 35-40.
- "Evaluating Wiring in Older Minnesota Homes," Agricultural Extension Service, University of Minnesota, St. Paul, Minnesota 55108.
- "Electrical Systems," A Training Manual for Home Inspectors, Alfred L. Alk, American Society of Home Inspectors (ASHI), 1987, available from ASHI. [DF NOTE: I do NOT recommend this obsolete publication, though it was cited in the original Journal article as it contains unsafe inaccuracies]
- "Basic Housing Inspection," US DHEW, S352.75 U48, p.144, out of print, but is available in most state libraries.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- Recommended books on electrical inspection, electrical wiring, electrical problem diagnosis, and electrical repair can be found in the Electrical Books section of the InspectAPedia Bookstore. (courtesy of Amazon.com)
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